Nigeria has deployed extra troops and planes to search for the schoolgirls.

"We want to assure Nigerians that no stone will be left unturned in our determination to rescue these girls", Nigeria's Information Minister Lai Mohammed told the BBC.

Anger has been growing among the girls' parents amid reports that soldiers had been withdrawn from key checkpoints in Dapchi last month.

Dapchi, which is about 275km (170 miles) north-west of Chibok, came under attack last Monday, causing students and teachers from the Government Girls Science and Technical College to flee into the surrounding bush.

Residents say that Nigeria's security forces, backed by military jets, later repelled the attack.

Authorities initially denied the students had been kidnapped, saying they were hiding from their attackers.

But they later admitted that 110 girls were missing after the attack.

Boko Haram militants have been fighting a long insurgency in the country's north in their quest for an Islamic state in the region.

Nearly four years ago they abducted 276 girls from a school in Chibok, leading to a worldwide #BringBackOurGirls campaign. The location of more than 100 of those girls is still unknown.

The conflict is estimated to have killed tens of thousands of people, and led to the abduction of thousands.